CVE-2026-18220 Binutils: binutils: out-of-bounds write in bfd dlx elf backend relocation processing
Out-of-bounds write in binutils DLX backend allows arbitrary code execution when processing crafted ELF files, requiring the DLX backend to be enabled.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-18220?
CVE-2026-18220 is a high-severity memory corruption vulnerability in Red Hat Enterprise Linux 10, published on 29 Jul 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Official description
An out-of-bounds write vulnerability was found in the BFD library's DLX ELF backend (bfd/elf32-dlx.c) in GNU binutils. The dlx_rtype_to_howto() function maps ELF relocation types to internal howto structures but fails to perform adequate bounds checking on attacker-controlled relocation type values (via ELF32_R_TYPE(r_info)) before indexing into the dlx_elf_howto_table[] array. The DLX relocation type number space is non-contiguous (basic types 0-6, extended types at 0x10000+), but the default case in the switch statement allows arbitrary index values to reach the array access.
A specially crafted ELF/DLX object file can trigger this out-of-bounds write when processed by any BFD-consuming tool (objdump, readelf, strip, ld, nm, objcopy). The vulnerability has been demonstrated to achieve arbitrary code execution via a File Stream Oriented Programming (FSOP) attack against glibc FILE structures (stderr), redirecting control flow to system().
Attack scenarios include CI/CD pipelines performing automated binary analysis, developer workstations running objdump/readelf on untrusted binaries, automated security scanning or malware analysis tools invoking binutils, and package build systems processing third-party code.
Note: This vulnerability is only exploitable when binutils is built with the DLX backend enabled (typically via --enable-targets=all).
Weakness: CWE-787
Which versions are affected by CVE-2026-18220?
How do I fix CVE-2026-18220?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-18220 being exploited?
There is no known exploitation of CVE-2026-18220 in the wild and no public exploit code.
Public exploit code: 1 proofs of concept on GitHub.
Sources
Also known as DEBIAN-CVE-2026-18220, GHSA-9x84-fgv4-3chj.